MEMS devices are a combination of micro mechanical and micro electronic systems that are revolutionizing nearly every product category by bringing together these systems. A MEMS device typically includes a movable micro mechanical structure and silicon based microelectronics. One type of known MEMS device is a MEMS transducer. Capacitive MEMS transducers may be used in an air-bag system for crash detection. For example, a crash is detected by monitoring the movement of the mechanical structure in the MEMS transducer using associated microelectronics in the MEMS transducer. The mechanical structure in the transducer often includes a dynamic capacitive plate which is positioned relative to a fixed capacitive plate. The capacitance between the capacitive plates depends, at least in part, on the distance there between. As the dynamic capacitive plate is displaced, a change in capacitance is caused by the relative change of the dynamic capacitive plate relative to the fixed capacitive plate. This change in capacitance is detected by the microelectronics. If the change is sufficiently large and/or abrupt, the microelectronic activate the air bag.
Micro electrical mechanical systems (MEMS) can also be used to create pressure sensors that are small and sensitive. These sensors have traditionally been used in aircraft testing, fluid mechanics experiments, sensor arrays, hearing aids, and other applications where small sensors of pressure or vibration are desired.
MEMS transducers are frequently manufactured from a single wafer. The mechanical structure of these transducers is created by depositing a poly-silicon layer on a silicon wafer, which is typically only a few microns thick. Many existing MEMS pressure sensors require integration with CMOS circuitry or require complex manufacturing techniques such as bonding multiple substrates. Complex manufacturing techniques require expensive machinery and materials and potentially lower the yield of functional devices.
MEMS pressure sensors have also been manufactured using piezoresistors attached to a diaphragm. Piezoresistors are inexpensive to manufacture and can be built with standard silicon wafer processing. However, the sensitivity of these devices is limited by the small amounts of strain generated by MEMS diaphragms.